1. Technical Field
The present invention relates to a high-intensity light generation engine and associated light transmission apparatus for transmitting the light generated by the engine to a remote location. The invention is especially applicable for use in constructing a back lighted display, such as a liquid crystal display (LCD), of minimal thickness. In particular, the invention achieves a display of minimal thickness by separating the light source from the display mechanism. Such a display is most suited for use in high ambient lighting conditions where space is at a premium, such as in the cockpit of an aircraft. The inventive light generation engine and associated light transmissive apparatus may also be used for other applications besides illuminating a display, such as for projection displays, ground vehicle instrument displays, automotive lighting (such as headlights, tail lights, panel lights, map lights, and dome lights), airport runway lights, aircraft interior lighting, and street lights.
2. Background Art
Typically, high luminance displays (e.g. those used in avionics applications) are based upon transmissive liquid crystal displays (LCDs) with one or more fluorescent lamps. When packaged in a reflecting cavity and supplemented by light control films, such lamps can be driven at sufficient power levels to generate enough lumens to produce well in excess of 200 fL out of the transmissive LCD. Typically, these displays are at least three inches thick when combined with a minimal amount of electronics. As more electronics are added to increase functionality, display thickness increases correspondingly. Additionally, for avionics applications, the active display area must occupy a large percentage of the overall enclosure area since instrument panel space is at a premium. This further complication increases packaging density, and as the packaging density increases, the thermal design obviously becomes more critical. Beyond approximately 0.1 watts per cubic inch, active cooling should be employed, which is generally fan-based, thus further increasing volume.
There exists a desire to drive the display thickness to less than one inch for many applications, such as avionics. For avionics applications, this would facilitate upgrading a cockpit with new displays requiring minimal modification of the cockpit instrument panel and surrounding structural members. Obsolete displays may be removed and replaced by new displays, including those which relate to the present invention, that simply attach over the existing instrument panel. Most avionics displays protrude in front of an instrument panel by no more than one inch. This limitation is due to several factors, such as the need to preclude one display from shadowing another. Another consideration is that displays cannot protrude into the xe2x80x98ejection envelopexe2x80x99 in fighter and attack planes and also cannot interference with the controls used by a crewmember (such as, for example, limiting full travel of the control yoke).
To achieve high luminance, high contrast, and high resolution in a conventional display intended for high ambient lighting conditions, considerable display thickness and relatively high-intensity light sources are required. However, thick displays and the large amounts of heat generated by high intensity lamps are adverse to certain applications, such as those for the cockpit of an airplane.
In view of the foregoing, this invention provides a display system in which the light source is located remotely from a display device, such as an LCD, and its backlight. By separating the lamp, driving electronics and other components from the display device and locating them remotely, space requirements can be satisfied without violating the severe envelope restrictions for aircraft cockpit-suitable display system elements.
This invention also provides a high-intensity light engine comprising a light source and a light collection assembly, and an optical transmission apparatus for transmitting the light to a remote location, such as to a display device.
The present invention is directed to a high-intensity light generation engine and associated light transmission apparatus for transmitting the light generated by the engine to a remote location. The invention is especially applicable for use in constructing a back lighted display, such as a liquid crystal display (LCD), of minimal thickness, i.e., one-inch or less. A display of minimal thickness is achieved by separating the light source and other peripherals from the display device. Accordingly, the light source and other light transmissive apparatus are comprised in a remote enclosure. Such a display is most suited for use in high ambient lighting conditions where space is at a premium, such as in the cockpit of an aircraft. The inventive light generation engine and associated light transmissive apparatus may also be used for other applications such as projection displays, ground vehicle instrument displays, automotive lighting, airport runway lights, aircraft interior lighting, and street lights.
In accordance with an illustrative embodiment of this invention, a system for illuminating a display, such as a flat panel display (i.e. an LCD) is provided. Several of the systems functional elements are illustratively listed below:
A light source for generating light.
A light collection assembly for collecting the light generated by the light source and for providing one or more light outputs. The light-collecting assembly comprises at least one ellipsoidal mirror, and preferably eight ellipsoidal mirrors, for reflecting the light generated from the light source to corresponding exit port holes.
A light guide assembly for collecting light from the light output(s) and transmitting it to a common exit port.
An optional dimmer for providing a controllable variable attenuation of the light emitted by the light guide assembly common exit port.
A homogenizer for capturing potentially non-uniform light from the optional dimmer or, alternatively, directly from the light guide assembly common exit port, and for providing a uniform irradiance across the homogenizer exit port area. The irradiance across the exit port area generated by the homogenizer also has uniform spectral and angular characteristics. Note that the homogenizer is preferably tapered, where its input port is larger than its output port.
A fiber optic cable assembly for capturing light from the homogenizer exit port and distributing it to multiple exit ports.
A collimator element assembly. Each collimator element captures light from a corresponding light distribution means exit port and projects light with improved collimation.
A turn-the-corner assembly that captures the collimated light projected by the collimator elements and reverses its propagation direction in a space-efficient manner while maintaining collimation.
A waveguide backlight that captures the collimated light from the turn-the-corner assembly and projects it in the direction normal to the backlight exit face.
A liquid crystal display (LCD) that transmits the collimated light projected by the backlight while modulating it spatially and, in non-monochrome applications, spectrally across the LCD area to form an image.
A view screen that transmits the light projected by the LCD while decollimating (or diffusing) it to project the LCD image to be seen over a wide range of viewing angles.
As an aspect of this embodiment, the system further comprises one or more optical light pipes (e.g., a solid cylindrical rod or, alternatively, a square or rectangular cross section solid rod), where each light pipe is coupled to a respective exit port hole of the light-collecting assembly. The light pipes reduce heat concentrations and ultraviolet radiation, generated by the light-collecting assembly, which would otherwise be fully dissipated in the light guides leading to the homogenizer. The light pipes are preferably made of a visible light transparent heat-tolerant material, such as glass, fused silica or sapphire. Further, each light pipe is preferably coated with either a dielectric infrared-reflecting coating, an ultraviolet reflecting coating or a combination thereof.
As a further aspect of this embodiment, the waveguide has a bottom surface having either a sawtooth or a truncated sawtooth surface for directing light out of the waveguide at predetermined angles based on the size and shape of the sawtooth and truncated sawtooth surfaces.
As an additional aspect of this embodiment, the system includes an apparatus for redirecting light, such as a turn-the-corner prism assembly, positioned preceding the waveguide. Illustratively, this assembly has one or more prisms, where each prism includes an input surface, an output surface, and in the case where there are a plurality of prisms, an interface between the prisms (such as a thin adhesive or glue gap) to improve the light-handling efficiency of the assembly. In particular, the adhesive preferably has an index of refraction less than the index of refraction of the adjacent prisms.
The system also includes an electromechanical dimmer for attenuating the light entering the homogenizer. The dimmer disposed immediately preceding the homogenizer entrance port is configured to have a dimming ratio from 300:1 to 88,500:1. The dimmer comprises a pair of aperture plates, where each plate has a diamond-shaped aperture. One of these may include a filter therein. However, differently shaped apertures can also be configured to provide the same function.
As yet a further aspect of this embodiment, the system further includes an array of collimators, positioned immediately preceding the turn-the-corner prism assembly, for collimating the homogenized light. Illustratively, the collimator comprises an array of tapered cavities, where the array""s tapered cavities have either round, square, or triangular cross-sections, or combinations thereof.